The present invention relates to a fuel pump and in particularly to a gasoline use fuel pump suitable for an in-cylinder direct injection system used for in an internal combustion engine.
In an internal combustion engine, in particular in a gasoline internal combustion engine for use in an automobile, from aspects of an improvement of fuel consumption property, a reduction of harmful exhaust gas and an improvement of driveability (a response for a drive condition changing) etc. of the automobile, in recently a practical application about an in-cylinder direct injection system used in an internal combustion engine is seriously studied.
In the in-cylinder direct injection system of the gasoline internal combustion engine, a fuel delivery source is indispensable to directly inject the gasoline into a cylinder of the gasoline internal combustion engine. Since the gasoline injection into the cylinder requires to carry out even during a compressing period of the engine, from the above stated fuel delivery source, it is necessary to delivery the fuel having a high pressure of some 30-100 kg/cm.sup.2.
The gasoline to be delivered has an extremely small viscosity property and also has an inferior lubrication property in comparison with general use oil such as engine oil.
As a result, since the leakage of the gasoline from a compressing part is large and it is difficult to compress the gasoline at a high pressure, a lubrication property in a load supporting member (for example, a bearing member) for necessarily constituting a fuel pump construction is injured.
At the present time, it is a problem wherein the bearing member enable to use one having the sufficient life time can not be expected under the gasoline environment.
Further, in a sealing member of a rotative shaft for necessarily constituting the fuel pump construction, at the present time, it is extremely difficult to expect the sufficient reliability property of the sealing member under the gasoline environment.
From the above stated circumferences, a fuel pump as a prior art is disclosed in, for example, Japanese patent laid-open publication No. 209,981/1992.
In this conventional fuel pump construction, concerning the above stated problems about the low gasoline viscosity property and the difficult compression to the high pressure, following problems for realizing the fuel pump are solved.
Namely, in the above stated conventional fuel pump construction using the secondary fluid having the high viscosity and the high lubrication property, an ascend pressure in the fluid is easily performed.
The gasoline being an objective material is raised in pressure through a pressure transfer member (in this case, a bellows) and in addition to the above the lubrication in the load supporting member such as a bearing member is performed using the secondary fluid. Further, the secondary fluid becomes a sealing objective matter for sealing a rotative shaft.
However, in the above stated conventional fuel pump construction, since the pressure transfer member is necessary to provide every compressing cylinder of the fuel pump each, a number of components increases. Further, from a structural aspect in case of an employment of a multi-cylinder structure, since the above stated apparatuses are necessary to arrange toward an axial direction, therefore it causes a problem where an axial direction dimension of the fuel pump construction increases.
In the above stated in-cylinder direct injection system for use in the internal combustion engine, from aspects of the volume control accuracy of the injection fuel, the response for control, the security of a degree of freedom in an injection timing optimization, it is desirable to electronically perform a control of an injector. To serve the above purpose, it requires a small fluctuation of a delivery fuel pressure.
Accordingly, it is desirable to provide a large number of the compressing cylinders and in case of the multi-cylinder structure it is desirable to realize a compact size fuel pump structure.